Previous studies in our laboratory have shown that progressive hypertension develops in dogs exposed for 14 days to avoidance conditioning schedules and increased intake of salt and water. The hypertension is accompanied by no consistent changes in heart rate levels. Typically, hypertension does not develop in dogs exposed to avoidance schedules under conditions of normal sodium intake, or to salt loading of non-stressed dogs over comparable time periods. The present research investigates the role of selected physiological systems presumed to participate in the development of this new model of exprimental hypertension. Studies are designed to evaluate changes in sodium and fluid balance, renal blood flow and resistance, stroke volume, cardiac output and total peripheral resistance occurring under conditions of avoidance schedules and saline infusion. The role of the sympathetic nervous system in the mediation of avoidance-saline hypertension will be evaluated by measurements of the effects of pharmacological blockade of sympathetic nervous system activity on blood pressure and other cardiovascular variables. In addition, adaptations of adrenal hormones to avoidance-saline hypertension will be assessed by periodic sampling of blood levels under these conditions. Experiments are also designed to evaluate the antihypertensive effects of behavioral procedures which prevent acute increases in total peripheral resistance and/or reductions in renal blood flow upon cardiovascular adaptations to avoidance schedules and saline infusion. These experiments may clarify the role of environmental and behavioral factors in the pathophysiology of sustained hypertension, and provide direction for development of nonpharmacological interventions in human hypertension.